The invention relates to a matrix display device for displaying luminance values, wherein a common value is determined for a group of lines and addressed simultaneously to said group of lines. This is performed, for example, when said luminance values are coded in subfields and some of the least significant subfields are replaced by a common value.
The invention also relates to a method of determining new luminance values based on original luminance values to be displayed on a matrix display device.
The invention is applicable in, for example, to plasma display panels (PDPs), plasma-addressed liquid crystal panels (PALCs), liquid crystal displays (LCDs), Polymer LEDs (PLEDs), Electroluminescent (EL), Digital Micromirror Devices (DMDs), used for personal computers, television sets and so forth.
A matrix display device comprises a first set of data lines (rows) r1 . . . rM extending in a first direction, usually called the row direction, and a second set of data lines (columns) c1 . . . cN extending in a second direction, usually called the column direction, intersecting the first set of data lines, each intersection defining a pixel (dot).
A matrix display device furthermore comprises means for receiving an information signal comprising information on the luminance values of lines to be displayed and means for addressing the first set of data lines (rows) r1, . . . rN in dependence on the information signal. Luminance values are hereinafter understood to be the grey level in case of monochrome displays, and each of the individual levels in colour (e.g. RGB) displays.
Such a display device may display a frame by addressing the first set of data lines (rows) line by line, each line (row) successively receiving the appropriate data to be displayed.
In order to reduce the time necessary for displaying a frame, a multiple line addressing method may be applied. In this method, more than one, usually two, neighbouring, and preferably adjacent lines of the first set of data lines (rows) are simultaneously addressed, receiving the same data.
This so-called double line addressing method (when two lines are simultaneously addressed) effectively allows speed-up of the display of a frame, because each frame requires less data, but this is at the expense of a loss of the picture quality with respect to the original signal, because each pair of lines receives the same data, which induces a loss of resolution and/or of sharpness due to the duplication of the lines.
These known methods allow a reduction of the addressing time. However, there may be a difference, and in some instances a large difference, between the original luminance values to be displayed and the new luminance values actually displayed. This difference, induced by the line doubling or grouping, herein called xe2x80x9cerrorxe2x80x9d, causes a loss in spatial resolution, and increases visible noise-like artifacts, comparable to quantization.
For the above-mentioned matrix display panel types, the generation of light cannot be modulated in intensity to create different grey scale levels, as it is the case for CRT displays. On said matrix display panel types, grey levels are created by modulating in time: for higher intensities, the duration of the light emission period is increased. The luminance data are coded in a set of subfields, each having an appropriate duration or weight for displaying a range of light intensities between a zero and a maximum level. The relative weight of the subfields may be binary (i.e. 1, 2, 4, 8, . . . ) or not. This subfield decomposition, described here for grey scales, will also apply hereinafter to the individual colours of a colour display. Line doubling or grouping is particularly useful in display panels using subfields, in order to reduce the addressing time.
In order to reduce loss of resolution, partial line doubling, i.e. line doubling for only some less significant subfields (hereinafter referred to as LSB subfields), can be performed. Indeed, the LSB subfields correspond to a less important amount of light, and partial line doubling will give less visible loss in resolution.
When more than two lines are addressed simultaneously for some less significant subfields, partial line grouping is performed. Considerations about partial line doubling will hereinafter also apply, mutatis mutandis, to partial line grouping of more than two lines.
In performing the partial line doubling method, a compromise must be sought. Only a few LSB subfields doubled would give a little gain of time. Too many subfields doubled would give an unacceptable loss of picture quality.
Another aspect that influences the quality is the method of calculating the new data of doubled subfields. Different calculation methods giving different results can be used. The method used should give the best picture quality, as seen by the observer""s eyes.
As the LSBs are doubled in partial line doubling, the value of the LSB data for two neighbouring or adjacent lines must be the same. The following methods may be used for the calculation of these data:
1. The LSB data of odd lines is used on the adjacent even lines (simple copy of bits).
2. The LSB data of even lines is used on the neighbouring or adjacent odd lines (simple copy of bits).
3. The average LSB data of each pair of pixels is used for both new LSB values.
It is an object of the invention to provide a matrix display device with line doubling or grouping, and a method of calculating new data to be displayed on said matrix display device where loss of resolution and/or visibility of noise-like artifacts is reduced, and preferably minimised.
To this end, a first aspect of the invention provides a matrix display device as defined in claim 1, providing a diffusion of the error induced by the line doubling or grouping either to neighbouring pixels to be displayed in the current frame and/or to neighbouring pixels of a subsequent frame. The visible error induced by line doubling or grouping is thereby reduced. Dependent claims 2 to 4 provide a specific diffusion of the error to the right-hand pair or group of pixels, the pair or group of pixels immediately below the one considered, and the same pair or group of pixels in the subsequent frame, respectively. Diffusing the error to the right-hand pair or group of pixels diffuses the error to the nearest pixels.
Simple embodiments, requiring a small number of components when implemented in hardware, are the subjects of depenent claims 2 to 4.
Dependent claim 2 relates to diffusion of the error to one or more neighbouring pixels on the same line.
Dependent claim 3 relates to diffusion of the error to one or more neighbouring pixels in a subsequent pair or subsequent pairs of lines.
Dependent claim 4 relates to temporal diffusion of the error to the same or neighbouring pixels.
Claim 5 relates to the case where luminance values are coded in subfields.
A second aspect of the invention provides a method as defined in claim 7. Dependent method claims 8 to 12 correspond to device claims 2 to 7, respectively.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiment(s) described hereinafter with reference to the accompanying drawings.